#include <stdint.h>
#include "tests/arc4.h"

/* Swap bytes. */
static inline void swap_byte(uint8_t *a, uint8_t *b)
{
    uint8_t t = *a;
    *a = *b;
    *b = t;
}

void arc4_init(struct arc4 *arc4, const void *key_, size_t size)
{
    const uint8_t *key = key_;
    size_t key_idx;
    uint8_t *s;
    int i, j;

    s = arc4->s;
    arc4->i = arc4->j = 0;
    for (i = 0; i < 256; i++)
        s[i] = i;
    for (key_idx = 0, i = j = 0; i < 256; i++)
    {
        j = (j + s[i] + key[key_idx]) & 255;
        swap_byte(s + i, s + j);
        if (++key_idx >= size)
            key_idx = 0;
    }
}

void arc4_crypt(struct arc4 *arc4, void *buf_, size_t size)
{
    uint8_t *buf = buf_;
    uint8_t *s;
    uint8_t i, j;

    s = arc4->s;
    i = arc4->i;
    j = arc4->j;
    while (size-- > 0)
    {
        i += 1;
        j += s[i];
        swap_byte(s + i, s + j);
        *buf++ ^= s[(s[i] + s[j]) & 255];
    }
    arc4->i = i;
    arc4->j = j;
}
